The sun's rays are known to produce ultraviolet radiation, such as sunburn that can have detrimental effects on the skin. Excessive exposure can lead to skin wrinkling, age spots, and even skin cancer. Skin cancer is the most common cancer diagnosed in the United States and the incidence of skin cancer continues to rise. Epidemiological studies have documented that extensive sun exposure increases the risk of developing non-melanoma skin cancer. Photo-protection is the primary preventative health strategy and sunscreens are one of the most important forms of photoprotection.
As people become more aware of the harmful effects of the sun, products such as sunless tanning products or self-tanning products are gaining popularity. These products typically employ a sunless tanning agent, such as dihydroxyacetone to impart color onto the skin that provides the impression of a tan produced by exposure to the sun. Many individuals have a skin complexion which does not tan readily on exposure to sunlight. Others achieve a tan only with great discomfort and possibly adverse effects to the skin due to exposure to sun's rays, e.g., sunburn. Yet, attainment of a tan is highly desired by many individuals for cosmetic and other reasons, especially if this can be accomplished effectively without the usual exposure to the sun, i.e., through skin-tanning agents.
In other instances, individuals who tan with difficulty may desire to enhance or extend the life of a naturally acquired tan without re-exposure to the sun. Also, a suntan may be desired when weather conditions do not permit the sun exposure necessary to acquire a tan. Acquisition of a natural tan by exposure to the sun may be almost impossible for those very light skin persons who tend to burn rather than tan, In addition, the deleterious effects of excessive exposure to sunlight are becoming more generally recognized.
It is known that an artificial tan can be achieved by applying skin-tanning agents to the human skin in a suitable vehicle or base. Examples of known skin-tanning agents include hydroxyaldehydes, such as dihydroxyacetone, (U.S. Pat. No. 2,949,403 and U.S. Pat. No. 5,232,688) and imidazole derivatives, such as 4-(hydroxymethylimidazole) (U.S. Pat. No. 5,252,322).
Dihydroxyacetone is reported to react with skin proteins and amino acids to elicit its skin coloring effect and many compositions using dihydroxyacetone as an active ingredient have been reported including topical composition further containing various dyes, such as catch powder, dogwood powder and walnut powder which are intended to offset the undesirable orange cast or hue which results from the use of dihydroxyacetone on fair skinned humans (U.S. Pat. No. 4,708,865). Other dihydroxyacetone compositions contain sunscreen compounds, such as octyl dimethyl PABA (U.S. Pat. No. 4,434,154 and U.S. Pat. No. 3,177,120). Further, dihydroxyacetone has been formulated into oil-in-water emulsions, into preparations containing up to 50% alcohol which tend to dry the skin, and into “creamy bases”, such as are found in hand and face lotions and creams. U.S. Pat. No. 5,232,688 discloses compositions for self-tanning of skin which include an alpha-hydroxy substituted ketone or aldehyde, such as dihydroxyacetone or erythrulose, a polyacrylamide, and a pharmaceutically-acceptable carrier.
There is a need for further sunless tanning agents and compositions comprising such agents.